/* Copyright (C) 2000 MySQL AB

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */

/* Synchronization - readers / writer thread locks */

#include "mysys_priv.h"
#if defined(THREAD) && !defined(HAVE_PTHREAD_RWLOCK_RDLOCK) && !defined(HAVE_RWLOCK_INIT)
#include <errno.h>

/*
  Source base from Sun Microsystems SPILT, simplified for MySQL use
  -- Joshua Chamas
  Some cleanup and additional code by Monty
*/

/*
 *  Multithreaded Demo Source
 *
 *  Copyright (C) 1995 by Sun Microsystems, Inc.
 *  All rights reserved.
 *
 *  This file is a product of SunSoft, Inc. and is provided for
 *  unrestricted use provided that this legend is included on all
 *  media and as a part of the software program in whole or part.
 *  Users may copy, modify or distribute this file at will.
 *
 *  THIS FILE IS PROVIDED AS IS WITH NO WARRANTIES OF ANY KIND INCLUDING
 *  THE WARRANTIES OF DESIGN, MERCHANTIBILITY AND FITNESS FOR A PARTICULAR
 *  PURPOSE, OR ARISING FROM A COURSE OF DEALING, USAGE OR TRADE PRACTICE.
 *
 *  This file is provided with no support and without any obligation on the
 *  part of SunSoft, Inc. to assist in its use, correction, modification or
 *  enhancement.
 *
 *  SUNSOFT AND SUN MICROSYSTEMS, INC. SHALL HAVE NO LIABILITY WITH RESPECT
 *  TO THE INFRINGEMENT OF COPYRIGHTS, TRADE SECRETS OR ANY PATENTS BY THIS
 *  FILE OR ANY PART THEREOF.
 *
 *  IN NO EVENT WILL SUNSOFT OR SUN MICROSYSTEMS, INC. BE LIABLE FOR ANY
 *  LOST REVENUE OR PROFITS OR OTHER SPECIAL, INDIRECT AND CONSEQUENTIAL
 *  DAMAGES, EVEN IF THEY HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH
 *  DAMAGES.
 *
 *  SunSoft, Inc.
 *  2550 Garcia Avenue
 *  Mountain View, California  94043
 */

int my_rwlock_init(rw_lock_t *rwp, void *arg __attribute__((unused)))
{
  pthread_condattr_t cond_attr;

  pthread_mutex_init(&rwp->lock, MY_MUTEX_INIT_FAST);
  pthread_condattr_init(&cond_attr);
  pthread_cond_init(&rwp->readers, &cond_attr);
  pthread_cond_init(&rwp->writers, &cond_attr);
  pthread_condattr_destroy(&cond_attr);

  rwp->state = 0;
  rwp->waiters = 0;

  return (0);
}

int my_rwlock_destroy(rw_lock_t *rwp)
{
  pthread_mutex_destroy(&rwp->lock);
  pthread_cond_destroy(&rwp->readers);
  pthread_cond_destroy(&rwp->writers);
  return (0);
}

int my_rw_rdlock(rw_lock_t *rwp)
{
  pthread_mutex_lock(&rwp->lock);

  /* active or queued writers */
  while ((rwp->state < 0) || rwp->waiters) pthread_cond_wait(&rwp->readers, &rwp->lock);

  rwp->state++;
  pthread_mutex_unlock(&rwp->lock);
  return (0);
}

int my_rw_tryrdlock(rw_lock_t *rwp)
{
  int res;
  pthread_mutex_lock(&rwp->lock);
  if ((rwp->state < 0) || rwp->waiters)
    res = EBUSY; /* Can't get lock */
  else
  {
    res = 0;
    rwp->state++;
  }
  pthread_mutex_unlock(&rwp->lock);
  return (res);
}

int my_rw_wrlock(rw_lock_t *rwp)
{
  pthread_mutex_lock(&rwp->lock);
  rwp->waiters++; /* another writer queued */

  while (rwp->state) pthread_cond_wait(&rwp->writers, &rwp->lock);
  rwp->state = -1;
  rwp->waiters--;
  pthread_mutex_unlock(&rwp->lock);
  return (0);
}

int my_rw_trywrlock(rw_lock_t *rwp)
{
  int res;
  pthread_mutex_lock(&rwp->lock);
  if (rwp->state)
    res = EBUSY; /* Can't get lock */
  else
  {
    res = 0;
    rwp->state = -1;
  }
  pthread_mutex_unlock(&rwp->lock);
  return (res);
}

int my_rw_unlock(rw_lock_t *rwp)
{
  DBUG_PRINT("rw_unlock", ("state: %d waiters: %d", rwp->state, rwp->waiters));
  pthread_mutex_lock(&rwp->lock);

  if (rwp->state == -1) /* writer releasing */
  {
    rwp->state = 0; /* mark as available */

    if (rwp->waiters) /* writers queued */
      pthread_cond_signal(&rwp->writers);
    else
      pthread_cond_broadcast(&rwp->readers);
  }
  else
  {
    if (--rwp->state == 0) /* no more readers */
      pthread_cond_signal(&rwp->writers);
  }

  pthread_mutex_unlock(&rwp->lock);
  return (0);
}

#endif
